Studies designed to determine the mechanisms of energy transduction and utilization in heart mitochondria will be conducted. Specific objectives will be to (1) Determine the effects of changes in concentration of extramitochondrial ADP and Pi and of inhibitors of oxidative phosphorylation on the steady state kinetics of the overall oxidative phosphorylation reaction (2) Further characterize the adenine nucleotide-induced inner membrane contraction phenomenon, (3) Develop a method for specific removal of loosely bound adenine nucleotides from mitochondria, (4) Determine the effect of changes in concentration of intramitochondrial adenine nucleotides on mitochondrial structure and function, (5) Determine the mechanism of energy-linked ion extrusion. The studies will be carried out with mitochondria isolated from slaughterhouse bovine hearts and will involve simultaneous monitoring of mitochondrial structure and function. Mitochondrial respiratory activity, mitochondrial optical density, and pH of the incubation mixture will be monitored simultaneously. State 3 rate of respiration will be used as an indicator of rate of oxidative phosphorylation and mitochondrial optical density as an indicator of change of inner membrane contractile status and of change of matrix volume due to influx and efflux of ions. Changes of mitochondrial structure and volume detected photometrically will be verified by electron microscopy and by determinations of mitochondrial packed volume.